1. Field of the Invention
The present invention relates to a rolling bearing which is subject to frequent occurrence of skidding due to operation at a high rotary speed and a low load, and more relates to a rolling bearing suitable for use as main shaft bearing for jet engine or gas turbine engine, bearing for external gear box and internal gear box of these engines or high-speed pinion bearing for them.
2. Description of the Related Art
In general, a rolling bearing comprising an outer ring, an inner ring and rolling elements. The rolling bearing is used in sites where some load is acted on.
However, when the rolling bearing is operated at a very small load (low load), a contact force of the rolling elements with respect to the raceway surface of the inner ring and the outer ring runs short, whereby skidding occurs therebetween.
When the rolling bearing is operated at a high rotary speed, the skidding occurs remarkably, causing abrasion called “skidding damage” on the slipping area between the rolling elements and the rolling surface of the inner ring and the outer ring. Accordingly, a life of the rolling bearing is drastically reduced.
In particular, a three point contact ball bearing comprises balls. The balls are kept in contact with one of the raceway surface of the outer ring and the inner ring at one point, and the other at two points. When the three point contact ball bearing is operated at a high rotary speed and a low load, skidding immediately occurs because the balls come in contact with the raceway surfaces at a relatively low constant pressure. Accordingly, this causes skidding damage that rapidly reduces the life of the bearing.
It is known that all the parts (outer ring, inner ring, rolling element) of a rolling bearing, which is operated at a high rotary speed and a low load, are made of heat-resistant bearing steel having a higher skidding abrasion resistance than ordinary bearing steel such as M50 (AMS6491: Aerospace Material Specification.
However, the rolling bearing cannot be certainly protected against skidding damage upon frequent occurrence of slipping because the bearing steel is not sufficiently resistant to abrasion.
In order to solve these problems, some approaches have been proposed. For example, the rolling elements of the aforementioned rolling bearing are made of ceramics. Alternatively, for bearings having rollers as rolling elements, the raceway surface of the outer ring is shaped ellipsoidal or triangular so that a pre-load is imposed on the rollers in order to certainly prevent the rolling bearing from slipping.
However, all these approaches are disadvantageous in that they cause a rise of production cost or complication of production process.